Strike and Dip
Geological structure is the study of the permanent deformation and rock failure created
by the changes in stress through geologic time. It is by far the most important aspect
of geology for the engineer to understand. Tectonic processes are responsible for the
many discontinuity planes (fractures, faults, joints) that permeate rock masses
controlling their strength, stress-strain characteristics and the transmission and
storage of fluids.
Structures may be conveniently subdivided into two groups:
The most striking features of rocks as engineering materials is that they are not
simple, isotropic, elastic and continuous but very complex, strongly anisotropic,
anelastic discontinuous. It is virtually impossible to deduce the stress history of
rocks from their observed deformation. There are always many ambiguous deformation
paths that could have been followed to produce what is observed.
- brittle structures - recording the brittle-elastic failure of rocks in the
past. Faults and joints fall in this broad category.
- ductile structures - preserving the permanent viscoplastic deformation of
rock throughout geologic time. Folds and metamorphic foliations are the expression of
this type of structure.
The study of structure involves the careful recording of the orientation of lines
and planes in rock masses in order to deduce the three-dimensional geometry of the
Strike and Dip
(c) Department of Civil and Geological Engineering, University of Saskatchewan,
57 Campus Drive, Saskatoon, SK, Canada, S7N 5A9